Patent application No. EP-1,681,337 A describes the conversion of feedstocks from renewable sources by decarboxylation in order to produce middle distillates. The advantage of this option consists in limiting the necessary hydrogen consumption. The method comprises an optional pretreatment stage followed by an isomerization stage using a catalyst containing a molecular sieve selected from among SAPO-11, SAPO-41, ZSM-22, ferrierite or ZSM-23 and a group VIII metal selected from among palladium, platinum and nickel, said method operating at a temperature ranging between 200° C. and 500° C., and at a pressure ranging between 2 and 15 MPa, the catalysts used being metallic catalysts. The diesel fuel base yields obtained with this method are however not maximized.
U.S. Pat. No. 4,992,605 describes a method of producing diesel fuel pool bases produced from the direct conversion of vegetable oils (rape, palm, soybean, sunflower) or lignocellulosic biomass to saturated hydrocarbons after hydrotreatment or hydrorefining of these products in the presence of a catalyst based on cobalt and molybdenum, at a temperature ranging between 350° C. and 450° C. and at a pressure ranging between about 4.8 MPa and 15.2 MPa. These conditions allow to obtain products with a high cetane number. The pro-cetane additives thus obtained are mixed with the diesel fuel in proportions ranging from 5 to 30% by volume. However, this method has the major drawback of involving a high hydrogen consumption due to the methanization or water-gas shift reactions. Besides, the oxygen contained in the triglycerides is generally decomposed by hydrodeoxygenation in the presence of a hydrotreating catalyst, which is costly in oxygen.
Patent application EP-1,741,768 describes a method comprising a hydrotreatment stage, followed by a hydroisomerization stage in order to improve the cold properties of the linear paraffins obtained, an intermediate stripping stage being preferably carried out. The catalysts used in the hydroisomerization stage are bifunctional catalysts consisting of a metallic active phase comprising a group VIII metal selected from among palladium, platinum and nickel, dispersed on a molecular sieve type acidic support selected from among SAPO-11, SAPO-41, ZSM-22, ferrierite or ZSM-23, said method operating at a temperature ranging between 200° C. and 500° C., and at a pressure ranging between 2 and 15 MPa. However, using this type of solid leads to a middle distillate yield loss for diesel fuel production.
One advantage of the invention is to provide a method allowing, from feedstocks coming from renewable sources, to obtain high diesel fuel base yields while allowing reduced hydrogen consumption.